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Full text of "Text Book Of Mechanical Engineering"

Appendix IIL

935

been thus treated from end to end by Prof. Weighton, and by
Mr. Leavenworth, and is here given in Fig. 888. Commencing at
A with the heat in the coal as roo % we find some 4 % of this lost

MCOAL

7?7rfrrr/T)
2.6-6

9M////

a

25-6

fltTl7}}j

-6    <

8***

I9-65--

q

-i-t

ffivyMZ^rtft, "mfr7ffifai0

I

\ <c

-QTTfM-   flSSOLC

r'2S     .
fOO        -

TOTAL

22

26



172.6

= 2^1



.68-

COAL    GRATE    BOILER    PIPE      DROP    CYLINDER  SHArr PROPELLER

FROM  BOILER   rURNACE   TO   <$H/P   PROPELLER

at the grate B due to incomplete combustion or dilution. A further
and very great loss occurs in the boiler at c on account of heat
passing up the funnel, leaving us with only 73 % of the original
heat to go to the steam pipe. A slight loss at D is caused by
radiation and condensation in the steam pipe, and 72*27 % is
given to the engine as dry steam. Now comes the great unavoid-
able natural loss on account of unavailability, present in all prime
movers, whether driven by heat, wind, or water, so that the
cylinder could not possibly give out more than '27 % of the steam-
pipe energy. On this amount, however, there is the loss by
initial condensation, which is very large, so that only 12*27 % of
the coal energy is ' indicated.' The final losses are the friction of
the engine and propeller shaft, and the slip of the propeller,
so that the ship is moved forward with only "0726% of the original
coal energy, supposing all the heat units to be available.

It does not appear, however, that the cylinder should be
specially debited with the loss by unavailability, and more probably
the best way is to deduct it from the coal energy in the first place.